How to: Enable Tarpitting to Reduce Spam
========================================

Tarpitting is when a server identifies a client’s abnormal email operations, and slows down or “tarpits” the process. 
Further information can be found `here <https://www.techopedia.com/definition/1722/tarpitting>`__.

With tarpitting enabled, if a sender attempts to issue commands to the mail server before the banner, the connection 
is dropped. Example:

.. code-block::

   [root@server ~]# telnet test.corp.interworx.com 25
   Trying 10.1.16.999...
   Connected to test.corp.interworx.com.
   Escape character is '^]'
   HELO test 554
   SMTP protocol violation
   Connection closed by foreign host.
   [root@server ~]#

Enabling both tarpitting and greylisting can be even more effective in reducing spam. Documentation on how to enable 
greylisting can be found :doc:`here </nodeworx/mail_server/spam_and_virus_protection/enable-greylisting-prevent-spam>`.

.. contents::

To Enable Tarpitting
--------------------

#. Log in to the server at the CLI as root, either via SSH or from the terminal
#. At the CLI, use the text editor to open ``/etc/tcprules.d/tcp.smtp``. By default, the contents of the file should look 
   similar to the following:

   .. code-block::

      127.:allow,RELAYCLIENT=""
      ::1:allow,RELAYCLIENT=""
      :allow,LANG="en_US",QMAILQUEUE="/var/qmail/bin/simscan",CHKUSER_MBXQUOTA="99" 

#. At the end of the line beginning with ``:allow``, add ``GREETDELAY="5",DROP_PRE_GREET="1"``

   .. code-block::

      127.:allow,RELAYCLIENT=""
      ::1:allow,RELAYCLIENT=""
      :allow,LANG="en_US",QMAILQUEUE="/var/qmail/bin/simscan",CHKUSER_MBXQUOTA="99",GREETDELAY="5",DROP_PRE_GREET="1"

#. Save and exit the text editor
#. At the CLI, run the command ``~vpopmail/bin/clearopensmtp``

   .. code-block::

      [root@server ~]# ~vpopmail/bin/clearopensmtp  
      [root@server ~]#